1. Field of the Invention
The present invention relates to a light amount control apparatus for use in a video camera or the like.
2. Description of the Related Art
In a video camera having CCD (charge-coupled device) elements, a light from an object is radiated through an optical lens onto an image pickup screen. The light from the object is photoelectrically converted into an electrical signal and the electrical signal is read out from the CCD element as a video signal by a read control signal from a read circuit. The video signal is corrected in shading and in various levels and then processed in a suitable signal processing fashion. Then, the thus processed video signal is output.
In such video camera, a light amount from the object is automatically adjusted and supplied to the CCD elements by a so-called auto iris mechanism. When the cameraman takes a picture of very bright scene, there is then the possibility that the iris is closed to the extent that an optical diffraction phenomenon will occur. Therefore, when the cameraman takes a picture of a scene brighter than the brightness corresponding to the position that the iris causes the above optical diffraction phenomenon, an ND (neutral density) filter that reduces a brightness is mounted on the video camera or the video camera is operated in the shutter priority mode where the shutter operation has a priority. Therefore, a sensitivity is intentionally reduced by the cameraman by a so-called electronic shutter which can vary an electric charge accumulation time in the CCD element.
When the ND filter is attached to the video camera in use or the electronic shutter is utilized intentionally, the user must attach or detach the ND filter to and from the video camera and also the user must determine whether or not the electronic shutter should be utilized. This is very cumbersome for the user.
However, if the ND filter is not utilized or the electronic shutter is not utilized when the cameraman takes a picture of such bright scene, a resolution is deteriorated due to an optical diffraction phenomenon. There is then the disadvantage that the cameraman cannot take a picture satisfactorily.
This phenomenon becomes remarkable when the sensitivity of the CCD element is increased. In order to solve the above problem, there is no other way than attaching the ND filter to the video camera or intentionally using the electronic shutter that is expected in other purpose.